JP3345138B2 - Flux for soldering - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering flux which can be used without removing a flux residue after soldering an electronic circuit board or the like.

[0002]

2. Description of the Related Art As a soldering flux, a resin obtained by adding an organic acid or an inorganic acid to a natural resin such as rosin is well known. However, in recent years, there has been a demand for abolition of cleaning of the flux residue from CFCs, and various flux compositions have been proposed that do not cause corrosion or decrease in insulation even if the flux residue is not cleaned and removed. For example,
Japanese Patent Application Laid-Open No. Hei 4-37497 discloses a method of uniformly dispersing an activator incorporated in a flux in a rosin to ensure electrical insulation and non-corrosion of a flux residue.
There is a disclosure that no cleaning of the flux residue can be achieved.

[0003] The rosin-based residue of the flux component slightly absorbs moisture in a high-humidity atmosphere, and its electrical insulation property is slightly reduced. Further, as compared with the case where the flux residue is present as a continuous film, the rate of decrease in insulation resistance is greater when cracks or peeling occur. It is considered that the reason is that dew condensation easily occurs in the cracks of the flux residue and a leak current path is formed.

[0004] To prevent cracking of rosin-based flux residue,
It is considered that the softening of the residue, that is, the use of a plasticizer, is effective. As a proposal of this kind, for example, Japanese Unexamined Patent Publication No.
No. 54298, a solder wire whose periphery was previously coated with rosin flux, and dioctyl phthalate as flux.
A method is disclosed in which a plasticizer such as dibutyl phthalate is blended to prevent the flux film from peeling off and falling off before soldering.

However, when these plasticizers are added to a rosin-based flux, the flux residue shows flexibility at a temperature of about room temperature, but at a low temperature of about -40 ° C. which is encountered in cold regions as electronic parts for automobiles. The generation of cracks cannot be prevented. Also, Japanese Patent Application Laid-Open No. Sho 60-13399
No. 8 discloses that properties such as solderability and detergency are improved by using a flux in which oxycarboxylic acid or an oxycarboxylic acid derivative having a molecular weight of 200 or more is added more than rosin. However, when this is used for the purpose of a non-cleaning flux, the flux residue does not crack, but the surface is sticky and foreign matter is likely to adhere. Therefore, a new problem such as a short circuit between the circuits on the substrate or a decrease in insulation resistance occurs.

Further, the activator contained in the flux is:
In order to maintain the activity, the use of various acids is indispensable, and the flux is usually used in an acidic state having a pH of less than 7. For this reason, cream solder, which is a kneaded product of solder alloy powder and flux, is liable to corrode the solder alloy, and if left in the air, the cream solder solidifies in a short time, making normal screen printing impossible. There's a problem.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is a rosin-based non-washable soldering flux in which flux residue after soldering becomes brittle at a low temperature. An object of the present invention is to provide a soldering flux that does not cause cracking, peeling, or the like.

[0008]

SUMMARY OF THE INVENTION The soldering flux of the present invention is a soldering flux containing a resin, oil and fat, a solvent and an activator, wherein the resin contains a rosin having a carboxyl group. Fats and oils have hydroxyl groups and-
Castor oil having a freezing point of 10 ° C. or less, and 50 to 9 parts by weight per 100 parts by weight of the rosin having a carboxyl group.
0 parts by weight, pH exceeds 8 by adding basic substance
11 or less .

The soldering flux of the present invention is formed mainly of a resin, oil and fat, a solvent and an activator as usual, and is used without cleaning the flux residue after soldering an electronic circuit or the like. Is what you do. The resin component is composed of rosins and may have a carboxyl group in the molecule, and for example, natural rosin, hydrogenated rosin, polymerized rosin and the like can be used.

[0010] fats and oils, as long as it has the following freezing point -10 ° C., rather particularly preferably castor oil having many hydroxyl groups in the molecule, purified castor oil, deodorized purified castor further
And modified castor oil. That is, castor oil has a main component of a derivative of oxy fatty acid and satisfies the above requirements. The oil has a solidification temperature of -10
If the temperature is higher than ℃, the flux residue after soldering has poor plasticity in a low-temperature environment and cannot prevent cracking.

As for the combination of rosin and fat, for example, in the case of a cream solder flux, castor oil is used for adjusting the viscosity of the cream. Therefore, the upper limit of the amount added is about 6% by weight based on rosin. In the present invention, the flux cannot be plasticized by the addition of a small amount as described above.
Add by weight. For this reason, the role of fats and oils in the flux is different from conventional ones. That is, the amount of the fat added is 5
If the amount is less than 0 parts by weight, the flux cannot be plasticized, and the flux residue is cracked at a low temperature and insulation failure is likely to occur, which is not preferable. On the other hand, when the addition amount of the fat or oil exceeds 90 parts by weight, the drying of the flux residue becomes insufficient, and the adhesion of the conductive foreign matter due to the stickiness of the surface deteriorates the insulating property.

If the flux contains a fat or oil having a hydroxyl group, such as castor oil, and a rosin having a carboxyl group, a slight esterification reaction occurs due to heating during soldering, and the two are combined. . Although this binding reaction is not preferable from the viewpoint of the plasticity of the flux residue, the reaction partially proceeds in the surface layer of the flux, so that the surface of the flux residue is in a dry state. For this reason, it is possible to prevent stickiness of the flux residue and crack prevention at a low temperature.

With the flux of the present invention in which fats and oils are added to rosin having a carboxyl group as described above, the cracking of the residue when left at low temperature can be suppressed remarkably, but the above effects are sufficiently exhibited in an environment where cold heat is repeatedly applied. Otherwise, residue cracking may occur. This is because the esterification reaction between the rosin having a carboxyl group and the fats and oils proceeded excessively due to the repetition of the cooling and heating. In such a case, the rosin having no carboxyl group is partially replaced by a rosin having no carboxyl group, that is, a rosin that has been esterified in advance, so that the composition does not change even after repeated cooling and heating. it can. In the present invention, a known rosin ester, for example, pentaerythritol ester of rosin, can be used as it is with or instead of rosin even in a normal flux. The ratio of this rosin ester is rosin with carboxyl group and rosin ester
If the rosins to which rosin is added is 100% by weight, the content is 60% by weight or less. If the amount of the rosin ester is larger than this, the flux residue becomes sticky, which is not preferable.

The pH of the flux is preferably from 7 to 11. Further, weak alkalinity of more than 8 and 11 or less is more preferable. The pH of the flux can be adjusted to 7 to 11 by adding a basic substance. The type of the basic substance can be used as long as it does not significantly impair the action of the activator during soldering. Particularly, those which easily evaporate or decompose at the soldering temperature are preferable, and amines are preferable. Further, among the amines, those having a boiling point not significantly higher than the soldering temperature are preferable. For example, in the case of a Pb-Sn solder that is soldered at around 230 ° C., it is preferable to use hexylamine (boiling point: 130 ° C.), octylamine (boiling point: 180 ° C.), or the like. In the region where the pH of the flux is less than 7, the effect of inhibiting corrosion of the solder alloy is poor, and corrosion occurs in the atmosphere. On the other hand, when the pH of the flux exceeds 11, the effect of inhibiting the corrosion of the solder alloy does not decrease, but since the amount of the basic substance increases, the proportion of the activator relatively decreases, and the spreadability of the solder decreases. Therefore, the pH of the flux of 7 to 11 is a practical region in which both the corrosion inhibiting action and the solder spreading property are compatible.

In the present invention, known activators, solvents and the like are blended as components other than the above-mentioned rosin and fats and oils. As the solvent, in addition to the solvent used for ordinary flux,
4-butanediol, 1,5-pentanediol, 1,
At least one of 6-hexanediol can be used. This diol enhances the ability of the flux residue to crack. When this flux is used for cream solder, a thixotropic agent or the like may be further added. The mixing ratio is not particularly limited, and the mixing ratio usually used can be applied as it is depending on the use form of the flux.

The type of the above-mentioned activator used in the flux of the present invention is not particularly limited, but those which volatilize at the soldering temperature and do not easily remain, and even if a little does not adversely affect the electrical insulation. preferable. For example, aromatic carboxylic acids, more specifically benzoic acid, salicylic acid,
Phthalic acid can be used. Although the flux of the present invention is suitable as a flux for cream solder, it can also be used as a general liquid flux or a flux for cored solder.

[0017]

The soldering flux according to the present invention is characterized in that a rosin having a carboxyl group in a resin and a solidifying temperature of -10 in oils and fats.
It contains a large amount of fats and oils below ℃. For this reason, the flux residue after soldering has plasticity even at a low temperature of −40 ° C., and the occurrence of cracks and peeling can be prevented. as a result,
Even if dew condensation occurs in the flux residue, it is possible to prevent a decrease in the insulation of the electronic circuit. Further, since the flux residue can be kept in a dry state, it is possible to prevent a decrease in insulation due to adhesion of conductive foreign matter.

Further, partial esterification reaction proceeds between the carboxyl group of rosin and the hydroxyl group of fats and oils due to heat at the time of soldering. In particular, the reaction easily occurs on the surface of the flux layer. The degree of drying on the surface is high, and circuit trouble due to adhesion of conductive foreign matter can be avoided. Further, by partially replacing the rosin with a rosin in which a carboxyl group has been esterified in advance, it is possible to enhance the drying of the residue and prevent the corrosion of the solder.

When the flux of the present invention is used as a flux for cream solder, the fats and oils act as a thixotropic agent and can improve printability. Further, the solidification of the cream due to the corrosion products is prevented, and the time until printing becomes impossible can be greatly extended. Further, since the flux of the present invention maintains low corrosiveness even after soldering, it has an effect of preventing corrosion of a soldered portion due to flux residue.

[0020]

The present invention will be specifically described below with reference to examples. (Example 1) Rosin having a carboxyl group, a resin having the composition shown in Table 1, castor oil as a fat, butyl carbitol as a solvent, and organic acids (phthalic acid, benzoic acid, sebacic acid, diphenylacetic acid) as activators After mixing) and hardened castor oil as an additive, respectively.
No. 1 and Comparative Example No.
Six kinds of fluxes of 10 to 12 were produced.

Each of the prepared fluxes is applied on a JIS type 2 comb-teeth electrode formed on a glass fiber reinforced epoxy resin substrate, and heated under a normal tin-lead eutectic solder reflow condition (maximum heating temperature 240 ° C.). After that, it was cooled.

[0022]

[Table 1] After that, the drying test of the flux residue was performed according to JIS Z319.
Based on No. 7, the presence or absence of chalk powder on the surface of the flux residue was examined. Table 2 shows the results. As shown in Table 2, each of the samples of Examples Nos. 1 to 3 had no chalk powder attached thereto, and no stickiness on the surface was observed.

In Comparative Example No. 10, the amount of castor oil was 40
Although there was little chalk powder adhesion by weight, no adhesion of chalk powder was recognized when the castor oil of No. 11 was equivalent to 100 parts by weight and rosin. In No. 12, when a rosin ester having no carboxyl group was used as the rosin of the resin, adhesion of chalk powder was observed. Therefore, in order to prevent stickiness of the surface, it is necessary to use a fat and oil having a coagulation temperature and the amount thereof and a rosin having a carboxyl group.

Next, each of the above samples was kept in a constant temperature bath at -40 ° C. for 30 minutes, taken out to room temperature, and observed with a microscope at a magnification of 25 times for the presence or absence of surface defects such as cracks in the flux residue. Table 2 shows the results. As shown in Table 2, in Examples Nos. 1 to 3,

[0025]

[Table 2] No crack was observed in the Lux residue. On the other hand, cracks were observed in Sample No. 10 with a small amount of castor oil. In an insulation resistance test performed thereafter, it was confirmed that the resistance value of No. 10 was lower by about one digit than that of other samples.

In Nos. 11 and 12, the flux residue was plasticized due to the large amount of castor oil added, and no cracks were observed as in the examples. (Example 2) Polymerized rosin was used as rosin, n-hexylamine was used as a basic substance, and oils, fats, solvents, activators, and additives were the same as in Example 1, and the procedure was the same as in Example 1. Four kinds of fluxes of Example Nos. 4 and 5 and Comparative Examples Nos. 13 and 14 were produced. Composition of each flux and p
H is shown in Table 3.

Each of the produced fluxes was subjected to the same residue cracking test and drying test as in Example 1. Table 4 shows the results. As shown in Table 4, no crack was observed in any of the flux residues, and no adhesion of chalk powder was observed. Next, apply each flux to JIS Z3197.
A solder spread test was conducted based on
Those with 5% or more were judged as good, and those with less than 85% were judged as bad. Conclusion

[0028]

[Table 3] The results are shown in Table 4. As shown in Table 4, the examples exhibited good solderability. With the flux of Comparative Example No. 14, the pH was as high as 11.2, so that the spreadability of the solder was poor. Next, a solder powder having a Pb-Sn eutectic structure is prepared,
10 parts by weight of each flux was added to 90 parts by weight and kneaded to prepare a cream solder. This was used as a sample for normal printing using a metal mask and a squeegee. In the printing process, printing was interrupted and left to stand in the printing process, and the time until printing became impossible due to solidification of the cream was measured.
The results are shown in Table 4 as printing durability time. From Table 4, pH7
In Comparative Example No. 13 using a flux of less than 3, the cream solidified after 4 hours, and printing was impossible. On the other hand, the creams using the fluxes of Examples Nos. 4 and 5 can be printed even after standing for 24 hours or more, and a significant improvement in printing durability was recognized. Note that Comparative Example No.
The printing durability of the cream using the flux having a pH of 11.2 was 48 hours or more, which is the same as in Examples 4 and 5, but the solder spreadability was not sufficient.

[0029]

[Table 4] Note: * Time according to JIS Z3137 ** Until printing cannot be performed by leaving cream solder in air (Example 3) Example No. 6 was performed in the same manner as Example 2 except that pentaerythritol ester of rosin was used as the rosin ester. And the flux of Comparative Examples No. 15 and 16 was produced. The pH of each of the obtained fluxes was 8.6.
８8.8. The prepared flux was applied on the same comb-shaped electrode as in Example 1 and reflowed. Thereafter, a drying test of the flux residue was performed. Table 5 shows the results. As shown in Table 5, in Example No. 6 and Comparative Example No. 15 containing no rosin ester, no chalk powder was adhered and no stickiness was observed on the surface. Comparative Example N
In the case of o16, the ratio of rosin ester was as high as 70%, so that chalk powder adhered. Next, each of the above samples was
A cooling / heating cycle test (1 cycle, 1 hour) was performed with 5 ° C. and −40 ° C. as upper and lower temperatures. After 100 cycles, the sample was taken out to room temperature and observed for cracks in the flux residue. As a result, as shown in Table 5, this Example No.
In No. 6, no crack was observed in the flux residue. On the other hand, cracks were observed in Comparative Example No. 15 containing no rosin ester.

[0030]

[Table 5]

Example 4 The procedure of Example 2 was repeated except that 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol were used as the solvent. Example Nos. 7 to 9 and Comparative Examples Nos. 17 to 19 No. 6
Seed flux was prepared. PH of the obtained flux
Was 8.6. The same test as in Example 3 was performed on the prepared flux. Table 6 shows the results. In the drying test, no chalk powder adhered to any of the flux residues. In the cooling / heating cycle test, no cracks were observed in the residues of Examples Nos. 7 to 9, but many cracks were observed in the residues of Comparative Examples Nos. 17 to 19.

[0032]

[Table 6]

[0033]

According to the flux for soldering of the present invention,
The oils and fats are in a state of being dissolved in the resin rosin, have plasticity, and can prevent cracking and embrittlement of the flux residue even at a low temperature of −40 ° C. For this reason, it is possible to prevent a decrease in insulation due to dew condensation or the like without cleaning and removing the flux residue. Therefore, it can be used as a soldering flux for electronic circuits for automobiles.

Further, due to heat at the time of soldering, a partial esterification reaction proceeds between the carboxyl group of the rosin and the hydroxyl group contained in the fat or oil, and the degree of drying on the surface of the residue increases. Therefore, there is no stickiness on the surface of the flux residue, and it is possible to avoid circuit trouble due to adhesion of conductive foreign matter. Furthermore, when the flux of the present invention is used as a flux for cream solder, the fat and oil act as a thixotropic agent and solidification of the cream by corrosion products is prevented, and the time until printability is reduced can be significantly extended. it can.

Continuing from the front page (73) Patent holder 591283040 Solder Coat Co., Ltd. 75-1 Nagata, Narumi-cho, Midori-ku, Nagoya-shi, Aichi Prefecture (72) Inventor Motoyasu Sugiura 1 Inside Toyota Central Research Institute Co., Ltd. (72) Inventor Eiichi Sudo 41-cho Yokomichi, Oku-cho, Nagakute-cho, Aichi-gun Aichi Prefecture Inside the Toyota Central Research Institute Co., Ltd. 41 at Yokomichi 1 in Toyota Central Research Institute, Inc. (72) Inventor Hiroshi Hamamoto 41 at Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Yokomichi 1 at Toyota Central Research Institute, Inc. No. 1 Toyota Motor Corporation (72) Inventor Hisao Shirai 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Hironobu Ono 1 Toyota Town Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Mitsuo Nakamura 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Kenichi Kawai 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Yasuhisa Tanaka 3 Midorigaoka, Toyota City, Aichi Prefecture 65-chome, Daitoyo Kogyo Co., Ltd. (72) Inventor Eiji Asada 3-65, Midorigaoka, Toyota-shi, Aichi Pref. Inside 72-chome Daitoo Kogyo Co., Ltd. (72) Inventor, Takehiko Narita Co., Ltd. (72) Inventor Hiromitsu Kojima 75-1, Nagata, Narumi-cho, Midori-ku, Nagoya-shi Inside Solder Coat Co., Ltd. (56) References JP-A-4-37497 (JP, A) JP-A-49-51145 JP, A) JP-A-61-95797 (JP, A) JP-A-60-133998 (JP, A) JP-B-63-17039 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , (DB name) B23K 35/363

Claims (3)

(57) [Claims] 1. A soldering flux containing a resin, a fat, a solvent, and an activator, wherein the resin contains a rosin having a carboxyl group, the fat or the oil has a hydroxyl group, and
Castor oil having a freezing point of 10 ° C. or less, and 50 to 9 parts by weight per 100 parts by weight of the rosin having a carboxyl group.
0 parts by weight, pH exceeds 8 by adding basic substance
A flux for soldering, wherein the flux is 11 or less . 2. The soldering flux according to claim 1, wherein when the rosin content is 100% by weight, not more than 60% by weight of the rosin is esterified rosin ester. 3. The solvent is 1,4-butanediol, 1,5
The soldering flux according to claim 1, wherein the flux contains at least one of -pentanediol and 1,6-hexanediol.